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Chemical Bonding

Chemical bonding is an important topic that many students struggle with and find difficult to grasp. It’s imperative to have your fundamentals clear and not have any confusion in your mind while understanding the concept of chemical bonding. Chemical bonding is one of the very important concepts of chemistry and helps in the study of material structures, properties, and reactions.

Today, in this article, we’re discussing chemical bonding and the various types of chemical bonding to help you give an edge over others when you study the topic in detail in your classroom.

So read on!

An Introduction to Chemical Bonding

The basic idea of chemical bonding is theoretical as it’s not a phenomenon that can be readily observed. The whole phenomenon of chemical bonding can be observed in the laboratory on a submicroscopic level.

Let’s try to understand the concept of chemical bonding in simpler terms.

Every object in our day-to-day life is made up of atoms and most of these atoms don’t exist just by themselves. These atoms are constantly working in conjunction with other atoms. While interacting with other atoms or groups of atoms, the atoms have a tendency to fill their outermost electron orbits. In other words, the atoms get arranged in the most steady shape or pattern that is possible. The resultant force holding the atoms together in groups (also called molecules) is generally referred to as Chemical Bonding.

At times, atoms can forge strong bonds and get arranged into molecules but they can also form weak or fragile bonds with other atoms. The existence of both, the strong bonds and the weaker bonds is important to maintain the chemistry of our bodies and to sustain life itself.

Why do Atoms Form Chemical Bonds?

The atoms always have a tendency to achieve a state of maximum stability possible. Most atoms gain stability when electrons fill their Valence Shells or by confirming to the Octet rule (i.e. by having eight valence electrons). In the absence of this desired situation, atoms will always strive to reach this ideal arrangement by sharing or losing electrons through the formation of bonds.

Types of Chemical Bonds

Now, let’s understand the type chemical bonds that exist. The chemical bonds can be classified into Ionic Bonds, Covalent Bonds, Hydrogen Bonds, and London Dispersion Forces.

Let’s take a look at each of these types of bonds individually and understand them in detail.

Ions and Ionic Bonds

Sometimes, atoms achieve greater stability by gaining or losing one or several electrons. In such a scenario, atoms make ions or particles that are charged. The gaining or losing of an electron or several electrons can lead to a filled outermost electron shell of the atom thereby making it more stable energetically.

Formation of Ions

Ions are atoms or molecules which have either gained or lost one or more electrons thereby lending the ion a net positive or a net negative charge. There are two types of ions; Cations and Anions. Cations are ions carrying a net positive charge and anions are ions carrying a net negative charge.  Hence, the basic difference between a cation and an anion is the ion’s net electrical charge.

Examples of a Cation Ion: Sodium: Na+, Hydronium: H3O+, and Ammonium: NH4+

Similarly, examples of an anion ion are: Hydroxide Anion: OH, oxide anion: O2-, and sulfate anion: SO42-

The following table outlines the differences between Cation and Anion ions on various parameters:

Parameter Cation Anion
Definition An atom or a molecule which is positively charged i.e. has a greater number of protons than electrons. An atom or a molecule which is negatively charged i.e. has a greater number of electrons than protons.
Type of Charge Positive Negative
Type of Electrode Used Cathode Anode
Type of Element Metal Non-Metal
Examples Sodium (Na+), Iron (Fe2+), and Lead (Pb2+). Sulfide (O2-), Fluoride (F-), Chloride (Cl-), Bromide (Br-), Iodide (I-), Nitride (N3-), and Hydride (H-).

In some cases, it is possible to foresee whether an atom will form a cation or an anion depending on its position on the periodic table. For example, Alkali metals and alkaline earth always form cations and most other non-metals always form anions.

Formation of Ionic Bonds

Since Cations and anions are positively and negatively charged, they usually form bonds. The resultant bonds coming into existence out of the mutual attraction of oppositely charged ions are called Ionic Bonds. The oppositely charged ions are bound to each other in such bonds.

Let’s look at everyday examples of such ions that are fundamental to the existence of life and the functioning of living organisms. In physiology, certain ions like sodium, potassium, and calcium are also known as electrolytes. The presence of these ions is absolutely necessary for the conduction of our nerve impulse, water balance, and muscle contractions. Many energy drinks and supplements are available in the market that provides these ions to replenish those lost from our bodies through sweating when we work-out.

Covalent Bonds

Covalent bonds are formed when atoms share electrons (instead of gaining or losing them) to become more steady. When atoms share one, two or three pairs of electrons between themselves, it results in single, double or triple bonds respectively. The strength of the bond depends on the number of electrons that are shared between two atoms. More the number of electrons shared between two atoms, the stronger the bond between them. Covalent bonds are more commonly found in the molecules of all living organisms and also in smaller inorganic molecules like H2O, CO2, and O2. The structure of carbon-based organic molecules like our DNA and proteins also rely on Covalent bonds.

Covalent bonds can further be classified into Polar Covalent Bonds and Non-Polar Covalent Bonds.

Let’s understand them in detail:

Polar Covalent Bonds

In Polar Covalent bonding, the pair of electrons is not equally shared between two atoms. The reason for this is that one atom enjoys a stronger pull than the other atom and thereby attracts electrons. Hence, in Polar Covalent Bonds, one atom spends more time with electrons than the other atom resulting in an unequal sharing of electrons.

Our lives literally depend on Polar Covalent Bonds because H2O or the water molecule is an example of a Polar Covalent Bond. In the case of a water molecule, the Oxygen atom attracts more electrons than the Hydrogen atom resulting in an unequal sharing of electrons. When an atom spends more time with electrons it results in the atom carrying a partial negative charge. Conversely, the atom that does not attract as many electrons carries a partial positive charge.

Another example of a Polar Covalent Bond is between a Hydrogen and Chlorine atom where the chlorine atoms attract more electrons than the hydrogen atom. This unequal sharing of electrons results leaves the chlorine atom with a negative charge and the hydrogen atom with a positive charge.

Non-Polar Covalent Bonds

Non-Covalent Bonds are formed when two atoms share a pair of electrons with each other. In Non-Covalent Bonds, two or more atoms are glued together to form a molecule by the shared electrons. Non-Polar Covalent Bonds are very strong bonds and a high amount of energy is required to break them.

Non-Polar Covalent Bonds form the oxygen that we breathe and help make up our living cells. In this sense, the study of Non-Polar Covalent Bonds is of paramount importance in Biology. The Peptide Bond is a type of Non-Covalent Bond that is extremely important in Biology as it binds the chains of amino-acids together. Amino-acids are crucial in the construction of our DNA and comprise of several atoms such as Oxygen, Carbon, Nitrogen, and Hydrogen.

Hydrogen and London Dispersion Bonds

Sometimes atoms or molecules can also form weaker or temporary bonds. While Covalent and Ionic Bonds are generally strong bonds, Hydrogen Bonds and London Dispersion Bonds are often considered the weaker bonds in Biology.

Let’s understand each of them in detail.

Hydrogen Bonds

In layman terms, a Hydrogen Bond is an attraction between a slightly positive hydrogen on one molecule and a slightly negative atom on another molecule. Hydrogen atoms are tiny and get really close to other atoms allowing them to get close to the slightly negatively charged unshared pair of electron of a nearby atom and form a bond with it. Hydrogen Bonds are the strongest of all intermolecular bonds and are crucial in affecting the properties of water and biological molecules like protein.

Hydrogen Bonds are found abundantly and water molecules in particular form plenty of them. Water is an excellent example of Hydrogen Bonding as it’s a polar molecule made up of two Hydrogens and one Oxygen. The Hydrogens are slightly positive while the Oxygen is slightly negative and the hydrogens form hydrogen bonds with the oxygen of adjacent molecules. Such bonds are weak by themselves but many hydrogen bonds together can be very strong.

London Dispersion Forces

London Dispersion Forces are weak bonds between molecules and can occur between atoms or molecules of any kind. These bonds are dependent on temporary imbalances in the distribution of electrons. Just like the Hydrogen Bonds, London Dispersion Bonds are weak attractions between molecules.

The London Dispersion Force occurs when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. London Dispersion Forces are responsible for the condensing of non-polar substances to liquids and to make them freeze into solids when the temperature is lowered sufficiently.

It would be impossible to sustain life without the presence of Hydrogen Bonds and London Dispersion Forces. Hydrogen Bonds are responsible for many life-sustaining properties of water and also for stabilizing the structures of proteins and DNA, both critical ingredients of cells.

Working of Bonds in a Cell  

Our bodies need both, the strong and the weaker bonds for a smooth functioning of the chemistry of our cells. On one hand, we need the strong covalent bonds to keep the chemical building blocks intact that make up a strand of our DNA. On the other hand, we need the weaker hydrogen bonds to keep the two strands of DNA helix intact. The weak bonds are critical for keeping the DNA stable and also for allowing it to be available for copying and use by the cell.

In the watery environment of a cell, the bonds between ions, water molecules, and polar molecules are constantly coming into being and breaking. In such a setting, the molecules of different types are bound to interact with each other through weak attractions based on their respective charges.

Properties of Ionic and Covalent Compounds

One of the often asked questions is: ‘How do you determine whether a compound is ionic or covalent merely by looking at a sample’?

Knowing the properties of ionic and covalent compounds can help answer this question. Since there are exceptions, you need to consider the various properties to come to a definitive conclusion whether a compound is ionic or covalent. Because of the different nature of the ionic and covalent compounds, the materials produced by them have varying macroscopic properties. The atoms of covalent bonds are bound tightly together in stable molecules but these molecules are not typically very strongly attracted to other molecules in the material. Conversely, the atoms in ionic materials display strong attractions to other nearby ions. This generally leads to low melting points for covalent bonds and high melting bonds for ionic solids.

Here are some of the properties of compounds that you need to keep in mind to make an informed decision:

  • Most crystals tend to be ionic compounds because the ions in such compounds stack into crystal frameworks to create a balance between the attractive forces of opposite ions and the repelling forces of the like ions. Although, covalent or molecular compounds can also exist as crystal. For example, sugar crystals and diamond.
  • Ionic compounds have higher melting and boiling points as compared to covalent compounds.
  • Ionic compounds are hard and brittle whereas covalent compounds are softer and relatively more flexible.
  • Ionics compounds are known to conduct electricity when dissolved in water whereas the same is not typically true for covalent compounds. The reason being, covalent compounds dissolve into molecules while ionic compounds dissolve into ions, which can conduct electrical charge.
  • Many ionic compounds are soluble in water but not in nonpolar liquid whereas many covalent compounds are soluble in nonpolar liquids but not in water.

Chemical bonds play a critical role in the world of Biology. They hold the cells in our bodies together and link almost everything around us on the atomic level. Chemical Bonds are the basis of most substances that exist, as well as the energy that powers them. Almost everything that we can see or touch including the air that we breathe, the food that we eat, the clothes we wear, etc. exist because of a chemical bond or many chemical bonds.

Hope you enjoyed reading this article and benefitted from it.

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